This invention relates to cathode ray tubes and more particularly to a means and method for processing the same to minimize processing incurred implosions.
Cathode ray tubes, such as those employed in both monochrome and color television and allied applications, are commonly fabricated with all-glass envelopes formed of an integration of viewing panel, funnel and neck portions.
During envelope fabrication and subsequent storage, handling and tube manufacturing, the surfaces of the envelope are vulnerable to accidental abrasion and scratching even though rigid quality procedures and controls are implemented. It has been found that the surface tensions produced in the glass envelope during particularly the tube exhaust procedure may become critical factors during the cooling portion of the process due to atmospheric pressure and temperature differences existent between the inner and outer surfaces of the envelope. Therefore, tubes having surface defects, in particularly the panel area, are apt to implode during tube exhaust processing because of these expansive and contractive forces induced in the glass during the heat cycle. In view of the possibility of the interaction of aggravative factors at abraded surface areas, attempts have been made to minimize the risk of implosions of such tubes by lengthening the critical cooling segment of the exhaust process. Thus, the excessive time required to provide an economically acceptable implosion level by slower cooling becomes a limiting factor in the rate of tube production and an additional manufacturing cost consideration. Despite efforts to minimize surface defects and the following of a lengthened exhaust cooling schedule, occassional implosions still occur during processing.
Economic losses incurred by tubes scrapped because of surface defects, implosions during processing, and increased costs incurred by slow or reduced rate of production are important factors consituting a perplexing problem encountered in cathode ray tube manufacturing.